Telephone receiving apparatus.



G. W. PIGKARD. TELEPHONE RECEIVING APPARATUS.

APPLICATION FILED MAR. 16, 1910.

Patented Oct. 11, 1910.

WITNESSES: I v INVENTOR Greenleaf VVhz'tlz'erPz'ckard l t I I 1- f ATTORNEY GREENLEAF WHITTIER PICKAIRIQD, or AMESBURY, MASSACHUSETTS.

Specification of Letters Patent.

TELEPHONE RECEIVING APPARATUS.

Patented Oct. 11, 1910.

Application filed March 16, 1910. Serial No. 549,688.

To all whom it may concern;

Be it known that I, GREENLEAF W, PICK- ARI), a citizen of the United States of America, and a resident of Ainesbury, Massachusetts, have invented certain new and useful Improvements in Telephone Receiving Apparatus, the principles of which are set forth in the .following specification and accompanying drawing, wh ch disclose the form of the invention which I now'consider to be the best ofthe various forms in which the principles of the invention may. be embodied.

My 'improvementscomprise, first, a ,protective device for the windings of telephonic receivers, this being es ecially useful in connection with receivers or wireless telegraphs or wireless telephones; and, second, means whereby the pole-piece and magnet system,

of a telephone receiver, may be ad usted, within minutestvariations, to and from the diaphragm of the receiver.v

In the accompanyin drawin s, F igure l is a sectional view, at Tine X-Y of Fig. 2,

of a receiver casing, showing especially the means for adjusting the, magnet and polepiece system to and from the diaph-ra m, and Fig. 2 is a top view (the cap and iaphragm'being removed) of a receiver, especially showing the use of two spark-gaps and the connection of a middle piece with the magnet.

Referring to the protective spark-gap apparatus, this comprises three spark-gap terminals, the outer terminals ((1 and c) being connected, as usual, with the telephone leads, L and L and with the windings, W

and W of the magnets about-the. pole-. A third terminal is provided, and. this (te middlevterminal b) is connected,

pleces,

by wire W with the steel magnet, Rand the pole-piece system. The object of this portion of my inventionis to-prevent ex- .cessive potent al either across the terminals,

(1 0](com1ected with leads L, L),- or betweentlie-magnet and pole-piecesystem (P) and said-terminals.

7 It has heretofore beencustoma'ry toplace protective ark-gaps, or lightning arresters,; a crosst e terminals of tele hones, and similar indicatinginstruments,' or the pur posejof preventing excessive potential across these terminals; but such rotective devices do not prevent the {deve opment of high potential between the wire 'windings of the telephone and the metal which forms the The inclusion, according to my invention,

of a middle terminal (6-), referred to, when connected with the pole-piece system (P, 9),

cures these disadvantages, because, as I understand thematter, an excessive potential existin between L (or L and the magnet and po e-piece system, will have an easy discharge path, at either the gap 03 or the gap 6.

If desired, the entire pole-piece and magnet system (P, p) may bemoved toward or 'from the diaphragm T, by means of the screw S. This permits theoperator to vary the sensitiveness of the receiver within any desired limits, the' maximum sensitiveness being obtained when the distance between the pole-pieces (p) and the diaphragm (T) is at the minimum. In the ordinary telephone receiver, the separation'between the pole-pieces and the diaphragm is fixed once for all, so that no varlation of sensitiveness can'be obtained.

"Further than this, it is not possible for the,

manufacturer to reduce the separation, to

that giving the maximum sensitiveness, for

the reason that if this were done any slight change in the temperature, or even a mechanical jar, will allow the diaphragm to pull down to and adhere to a pole-piece, thereby rendering the instrument inopera tive. In other words, the ordinary type of telephone receiver must be constructed with a comparatively large-separation, in order that it shall maintain its operativeness under all conditions of practice.

" In my improved form, the pole-piece may be adjusted as near to the diaphragm as the operator wishes, and if, by reason of any jar or change in the temperature, the diaphragm should pull down and adhere to the pole-piece, a fraction of a turn of the screw movin in the base-plate B, would release the iaphragm.

I claim:

1. In.a telephone receiver, the combination with a magnet,-of a winding therefor,

ofline-terminals electrically connectecl vith said system by way of spark-gaps.

4. In a telephone receiver, the combination with :1 magnet, of a Winding therefor,

electrically separate therefrom in respect of ordinary telephone currents; and means for protecting the Winding from discharges 0t excessivepotential to the magnet, said means consisting of spark-gap break-down paths.

for such discharges between the magnet and v uninsulate'd parts of the circuit of the Winding on the two respective sides of the Wlnding itself.

- GREENLEAF WHITTIER PIGKARD.

\Vitnes'ses:

EDWARD H RoWELL, MYRA S. RQWELL. 

